In recent years, it has become common to employ a heat reflecting glass having a low solar energy transmittance (a ratio of directly transmitting energy to incident solar energy) as a means to increase cooling efficiency of e.g. a vehicle such as an automobile. As a method to reduce the solar energy transmittance, a method of employing a colored glass or a method of coating a colored film which is excellent in the heat reflecting performance on a transparent soda lime glass or on a colored glass having a high transmittance, is available. The latter method is preferred from the viewpoint of the heat reflecting performance and recycling of the glass.
What are required for such a glass coated with a heat reflecting colored film, may, for example, be that the solar energy transmittance is low, the visible light transmittance is high as compared with the solar energy transmittance, it has sufficient durability for use for e.g. vehicles, it has a color tone which does not impair the design of e.g. vehicles, and it has a high sheet resistance. As a glass coated with a heat reflecting colored film which satisfies these requirements, a glass is known wherein an oxide film comprising cobalt oxide as the main component, at least 10 mass % (the ratio based on the total metal amount, the same applies hereinafter) of iron and at least 5 mass % of chromium, is formed in a thickness of from 10 to 50 nm by a spraying method.
However, such a glass has had a problem such that the film thickness, composition, etc. are non-uniform, and the yield is poor.
It is known in literatures to obtain, by a sputtering method, a glass having a film formed which comprises cobalt oxide as the main component and at least 5 mass % of iron oxide. For example, JP-A-9-30837 discloses a heat reflecting glass having a coating film of metal oxides formed with a metal composition such that cobalt: 65 to 96 mass %, chromium: 2 to 25 mass %, iron: 2 to 33 mass %, and a sputtering method is mentioned as a method for forming such a coating film.
However, in a magnetron sputtering method whereby the film-forming speed is remarkably higher than the conventional methods, which is suitable for a mass production of a film having uniform film thickness and composition and which is a sputtering method presently utilized industrially, an alloy target comprising cobalt and iron can not be practically used, since such an alloy target is a ferromagnetic material, whereby a magnetic flux of magnetron is hardly formed over the target surface. In the above publication, no specific disclosure is given with respect to a sputtering method, and only a spraying method is specifically described.
Heretofore, it has been common that a ceramic paste having a ceramic color composition formed into a paste, is screen-printed along the peripheral portion or the center portion of a window glass of an automobile, followed by drying and baking in a bending step. Such a ceramic color paste is baked e.g. along the peripheral portion of glass to form a colored opaque layer and thereby to be used for preventing deterioration of an adhesive by ultraviolet rays or to prevent the bonded portion from being seen through from outside the car. As such a ceramic color composition, one having a heat resistant coloring pigment mixed to a glass frit, is known and usually has a color tone of a black color or a dark gray color. Such a composition is called a black ceramic coating material.
However, when such a ceramic color paste is printed on a glass having formed by a spray method a conventional oxide film comprising cobalt oxide as the main component, at least 10 mass % of iron and at least 5 mass % of chromium, there has been a problem that unfavorable whitish coloration is likely to result.
Further, when a glass is used as e.g. a rear glass of an automobile, so-called silver printing is carried out, wherein a silver paste which is an exothermic material to prevent fogging, is linearly printed and baked. However, a conventional glass having formed by a spray method an oxide film comprising cobalt oxide as the main component, at least 10 mass % of iron and at least 5 mass % of chromium, has had a problem that coloration of this silver print is poor (such that it forms an antique red color).
Accordingly, the above-mentioned glass coated with a heat reflecting colored film, cannot practically be produced by means of a magnetron sputtering method, and the above-mentioned problems such as formation of non-uniformity in the case of the production by the above-mentioned spray method, unfavorable whitish coloration in ceramic color printing, and poor coloration of silver printing, have not been solved.
It is an object of the present invention to provide a glass coated with a heat reflecting colored film, which can be produced by a sputtering method, which is excellent in the uniformity of the film thickness and composition and which is excellent in heat reflectivity, and a process for its production. Further, it is another object of the present invention to provide a glass coated with a heat reflecting colored film, which is excellent in the uniformity of the film thickness and composition, which is free from unfavorable whitish coloration in ceramic color printing and which is excellent in coloration of silver printing.